“Blister packaging” is a common term used for packaging having a bottom part, typically referred to as the “blister film”, with a plurality of recesses formed therein (e.g., through vacuum forming or pressure forming) wherein a respective product piece (e.g., a consumable tablet or pill) is positioned and held therein. A cover, typically referred to as a “lidding foil” is placed over and sealed to the blister film about the perimeter of each recess.
There are basically three different types of blister packaging which relate to how the consumer is meant to retrieve the consumable from its respective recess within the sealed package: push-through type, peel-push type and lock type. In the “push-through” type of blister package, the consumer must use a finger to push against the malleable blister film at the location of a recess and continue pushing until the consumable in the recess is pressed against and breaks through the covering lidding foil. In the “peel-push” type of blister package, the consumer must first peel away an upper layer of a two layer lid stock to reveal the lower layer, and then push against the malleable blister film at the location of a recess and continue pushing until the consumable in the recess is pressed against and breaks through the lower layer of the lidding foil. The “peel-push” type package is considered more child-proof than the strictly push-through type due to the extra layer of the lidding foil. In the “lock” type of blister package, the consumer can only get access to the recess content by destructing the lidding material using a tool like a pair of scissors, a knife, nails, etc. The present invention is primarily directed to the push-through or peel-push blister packaging, although it is noted that push-through is considered an integral part of a peel-push package. The push-through type of blister packaging is the most common package type for consumables in pill or tablet form such as chewing gum or pharmaceuticals.
Present day push-through blister packaging is manufactured with a lidding foil (typically aluminum foil) to which a heat seal lacquer is applied using gravure coating process. In the gravure coating process, the lacquer adhesive (e.g., vinyl acrylic lacquer) is dissolved in a solvent and applied to a steel roll engraved with a pattern of micro dimples or “cells”. As the steel roll rotates, the cells on the surface pick up the lacquer either by passing through a bath of lacquer or by direct application of the lacquer to the steel roll. A roll of aluminum foil rolls a sheet of foil between the rotating steel roll and a rubber roll whereby a thin layer of the lacquer is transferred from the steel roll to the foil. The use of the gravure coating process thus allows a relatively thin layer of the lacquer to be applied to the lidding foil. The use of this process on push-through blister packaging lidding foils has therefore been the industry standard for many years since, if the foil sheet and/or the lacquer layer are too thick, the consumer would not be able to readily push and cleanly break through the lidding foil.
In an extrusion coating process, the adhesive is extruded through a die in the form of a molten polymer curtain that is applied to the continuously moving aluminum foil. If extruded too thinly, breaks within the curtain could cause voids, which could leads to breaches in the package seal. Present day peelable lidstock (e.g., as used in single serve food containers having a peel-away foil lid) is typically manufactured using either extrusion coating process, extrusion lamination process or gravure coating process. Extrusion coating/lamination employs different adhesives than are used in a gravure coating process, and the peel-away type of lidding foil is sufficiently thick to prevent inadvertent puncturing of the lid prior to opening the container. A thicker layer of sealant (as one gets with an extrusion coating process as compared to the gravure coating process) may therefore be used for peel-away lidding foils to ensure complete sealing, but is inadequate for push-through blister packaging application.
In present day push-through blister packaging, the blister film is typically formed from a polymeric material such as, for example, polyvinyl chloride (PVC), polyvinylidene dichloride (PVDC), a PVC/PVDC-combination, a PVC/PCTFE-combination or polystyrene (PS). During the packaging process, the consumables are placed in their respective recesses in the blister film and the lidding foil is positioned thereover. A heat press is then applied to seal the lidding foil to the blister film about the periphery of each recess to thereby seal the consumable within the package.
The polymers presently used for the blister film of the package either do not create a complete barrier to moisture and air, and/or they may contain plasticizers that are subject to blooming and can contaminate the consumable. Insufficient barrier properties allow moisture and air seepage into the package over time which shortens package shelf life. Also, contamination of the consumable by additive blooming may be harmful to human health. Some states such as California have recognized the potentially harmful effects of PVC in packaging for consumables and are considering enacting legislation prohibiting the use of PVC in food and pharmaceutical packaging. There is also concern that incineration of waste blister packages containing halogenated polymers can release toxic fumes into the environment.
There is thus presently a trend in the pharmaceutical industry toward the use of blister films made of materials which have better moisture and air barrier properties and are more inert than presently used polymeric blister films. Polychlorotrifluoroethylene (PCTFE), available from Honeywell under the trademark Aclar®, is one example of a material having these desirable properties. Cyclic olefin copolymers (COC) available from Topas Advanced Polymers represent another class of similarly suitable materials.
Unfortunately, for push-through type lidding foils, the heat seal lacquers presently used for push-through blister lidding foils exhibit difficulty adhering efficiently directly to PCTFE (Aclar®), COC, and other similar materials having the above beneficial properties. As such, it has been a practice in the industry, when making push-through blister packaging, to laminate the more beneficial PCTFE (Aclar®), COC, etc. to the less beneficial (and less expensive) PVC (or some other polymers such as polypropylene (PP), high density polyethylene (HDPE), linear low density polyethylene (LLDPE), and polystyrene (PS), for example) to form the blister film. One present day industry manufacturing method then takes the conventionally manufactured push-through lidding foil with heat seal lacquer and seals it to the PVC side of the blister film to which the heat seal lacquer can efficiently adhere. This of course means the PVC side of the blister film must face the lidding foil and thus be in contact with the consumable. While this practice provides the benefit of the barrier properties of the PCTFE (Aclar®), COC, etc., the possibility of additive blooming is still present since it is the PVC layer which is in contact with the consumable inside the package. The ability to seal a push-through lidding foil directly to PCTFE (Aclar®), COC, etc. or similarly beneficial material would thus provide both an improved barrier and contact of the consumable with an inert material.
In certain cases it would also be desirable to replace lidding material that contains aluminum foil with a paper-based material. It is much easier to print on a paper support and this offers a significant advantage. However, paper does not provide the barrier to moisture that is afforded by aluminum foil and consequently, in many cases the contents of the blister package would not be sufficiently protected.
A considerable amount of technology related to blister packaging has been described previously. For example, sealant materials useful for peel-away lidstock are described in US Patent Application Serial Nos. 2005/0159549, 2005/0249903, and 2006/00104022, the disclosures of which are incorporated herein by reference, such materials including polymeric compositions that consist essentially of: about 10 to about 80 weight % of at least one ethylene/alkyl (meth)acrylate copolymer; about 5 to about 60 weight % of at least one polyolefin; 0 to about 35 weight % of at least one tackifying resin; and 0 to about 35 weight % of a filler such as, for example, talc.
The sealant materials described in the referenced patent applications are asserted to be useful to the pharmaceutical industry in user-friendly blister packaging for drugs in the form of pills, tablets, capsules and the like, and also for non-drugs such as poisons, catalysts, cleaning compositions, batteries, and various other goods. They may also be employed to seal lidded containers containing products such as yogurts, puddings, custards, gelatins, fruit sauces, cheese spreads and dips, meats, frozen or refrigerated meals, and dry foods such as noodle and snacks. The described sealant materials employed in various packaging applications are also asserted to provide a good heat seal that can be easily peeled.
U.S. Pat. No. 4,211,326, the disclosure of which is incorporated herein by reference, describes a push-through blister package that comprises a metal foil and a sheet provided with thermoformed pockets that comprises, prior to thermoforming, a laminate structure having outer layers of polyvinyl chloride (PVC) and an intermediate layer of fluid compression rolled, partially oriented polymeric material, for example, high density polyethylene (HDPE).
U.S. Pat. No. 6,010,784, the disclosure of which is incorporated herein by reference, describes a paperboard laminate for pharmaceutical blister packaging that employs a blend of a hot melt adhesive such as ethylene vinyl acetate (EVA) and calcium carbonate that is capable of sealing to Aclar®.
US Patent Application Serial No. 2007/0224379, the disclosure of which is incorporated herein by reference, describes a peelable child-resistant pharmaceutical blister lidstock for peel-push blister packaging that comprises a first layer of white polyester, a second layer of adhesive, a third layer of foil, and a fourth layer of a coating of a heat sealant such as a vinyl acrylic.
US Patent Application Serial No. 2002/0193031, the disclosure of which is incorporated herein by reference, describes a laminate for blisters and pouches that comprises a metal foil having an uncoated surface which has been directly heat sealed to the surface of a polymeric web by an outer surface of the web, wherein the outer surface comprises a blend of an EVA copolymer and an additive that embrittles the copolymer at room temperature. The polymeric web may be a laminate that includes a polyolefin core and a second outer surface that may be a polychlorotrifluoroethylene. The laminate is asserted to be useful in producing press-through packages, where it will not peel open when tablets are pushed through it, and also in producing pouches, where it will peel.
US Patent Application Serial No. 2005/0058793, the disclosure of which is incorporated herein by reference, describes a coextruded multilayer heat sealant structure that comprises a first layer of a thermoplastic polymeric material, a second layer of low density polyethylene, and a third layer of a single site catalyzed polyethylene for use as a heat sealant layer, the heat sealant structure being laminated to a substrate such as aluminum foil.
U.S. Pat. No. 7,316,317, the disclosure of which is incorporated herein by reference, describes a package that comprises a polymeric base sheet such as PVC containing recesses and a sealing web that includes a metal foil adhered to a polymeric web, for example, polyethylene terephthalate (PET). The sealing web has strength sufficient to prevent a packaged item in a recess from being pushed through by pressure applied to the recess. A portion of the package where the base web is sealed to the sealing web includes lines of weakness that allow the packaged item to be pushed through the sealing web.
US Patent Application Serial No. 2006/0199022, the disclosure of which is incorporated herein by reference, describes a blister pack that includes a laminate of a metal foil adhered to a water permeable layer by an adhesive that can be softened on exposure to water. A packaged item cannot be pushed through the foil until the adhesive is softened by water, thereby allowing removal of the water permeable layer from the foil.
U.S. Pat. No. 6,224,973, the disclosure of which is incorporated herein by reference, describes a multi-layer sheet suitable as a sealable or peelable sheet specially used for closing foodstuff containers or blisters. This multi-layer sheet comprises a tie-layer between a substrate layer and a seal or a peel. This multilayer sheet is prepared by extrusion or coextrusion coating. This patent describes the beneficial use of mineral filler for achieving ease of peelability, but not does not describe how to provide ease of push-through for push-through blister packaging.
U.S. Pat. No. 5,145,737, the disclosure of which is incorporated herein by reference, describes a system for closure and subsequent opening of a sterilizable container, which is made up of a cover having a sealing layer, which bonds to the cover, and where the sealing layer is made of a polymeric material such as high density polyethylene, polypropylene and polyester and the container, at the point where the cover is sealed to the container, and is also made of the same polymeric material as the cover's sealing layer. An inert filler is incorporated into the sealing layer and can also be incorporated into the container where the cover and container are joined. However, this patent does not describe how to provide ease of push-through for push-through blister packaging.
US Patent Application Serial No. 2005/0077202, the disclosure of which is incorporated herein by reference, describes blister packages which are formed from multilayered films having a lid-stock film which is heat sealed directly to a fluoropolymer film. A polymeric base layer is adhered to a fluoropolymer layer via a first intermediate adhesive tie layer; a support layer is adhered to the fluoropolymer layer via a second intermediate adhesive tie layer; and a metallic foil layer is adhered to the support layer via a third intermediate adhesive tie layer. However, this patent also does not describe how to provide ease of push-through for push-through blister packaging.
While the above patents and applications describe various lidding foils, blister films, and sealants for blister packaging, neither the industry nor the prior patent publications above have provided paper-based lidding material for push-through blister packaging that can be formed by extrusion coating or by lamination and that provide good moisture barrier properties and that further can be sealed directly to a chloride-free blister film such as PCTFE (Aclar®), COC, or similarly environmentally benign material and can provide good push-through properties.